diff --git a/solution/0000-0099/0005.Longest Palindromic Substring/README.md b/solution/0000-0099/0005.Longest Palindromic Substring/README.md
index 11a6b7df01a67..c6c52ab64cd4f 100644
--- a/solution/0000-0099/0005.Longest Palindromic Substring/README.md	
+++ b/solution/0000-0099/0005.Longest Palindromic Substring/README.md	
@@ -277,6 +277,42 @@ public class Solution {
 }
 ```
 
+#### C
+
+```c
+char* longestPalindrome(char* s) {
+    int n = strlen(s);
+    bool** f = (bool**) malloc(n * sizeof(bool*));
+    for (int i = 0; i < n; ++i) {
+        f[i] = (bool*) malloc(n * sizeof(bool));
+        for (int j = 0; j < n; ++j) {
+            f[i][j] = true;
+        }
+    }
+    int k = 0, mx = 1;
+    for (int i = n - 2; ~i; --i) {
+        for (int j = i + 1; j < n; ++j) {
+            f[i][j] = false;
+            if (s[i] == s[j]) {
+                f[i][j] = f[i + 1][j - 1];
+                if (f[i][j] && mx < j - i + 1) {
+                    mx = j - i + 1;
+                    k = i;
+                }
+            }
+        }
+    }
+    char* res = (char*) malloc((mx + 1) * sizeof(char));
+    strncpy(res, s + k, mx);
+    res[mx] = '\0';
+    for (int i = 0; i < n; ++i) {
+        free(f[i]);
+    }
+    free(f);
+    return res;
+}
+```
+
 #### Nim
 
 ```nim
diff --git a/solution/0000-0099/0005.Longest Palindromic Substring/README_EN.md b/solution/0000-0099/0005.Longest Palindromic Substring/README_EN.md
index 4ac2610fb4e8e..e317ceda58ac4 100644
--- a/solution/0000-0099/0005.Longest Palindromic Substring/README_EN.md	
+++ b/solution/0000-0099/0005.Longest Palindromic Substring/README_EN.md	
@@ -275,6 +275,42 @@ public class Solution {
 }
 ```
 
+#### C
+
+```c
+char* longestPalindrome(char* s) {
+    int n = strlen(s);
+    bool** f = (bool**) malloc(n * sizeof(bool*));
+    for (int i = 0; i < n; ++i) {
+        f[i] = (bool*) malloc(n * sizeof(bool));
+        for (int j = 0; j < n; ++j) {
+            f[i][j] = true;
+        }
+    }
+    int k = 0, mx = 1;
+    for (int i = n - 2; ~i; --i) {
+        for (int j = i + 1; j < n; ++j) {
+            f[i][j] = false;
+            if (s[i] == s[j]) {
+                f[i][j] = f[i + 1][j - 1];
+                if (f[i][j] && mx < j - i + 1) {
+                    mx = j - i + 1;
+                    k = i;
+                }
+            }
+        }
+    }
+    char* res = (char*) malloc((mx + 1) * sizeof(char));
+    strncpy(res, s + k, mx);
+    res[mx] = '\0';
+    for (int i = 0; i < n; ++i) {
+        free(f[i]);
+    }
+    free(f);
+    return res;
+}
+```
+
 #### Nim
 
 ```nim
diff --git a/solution/0000-0099/0005.Longest Palindromic Substring/Solution.c b/solution/0000-0099/0005.Longest Palindromic Substring/Solution.c
new file mode 100644
index 0000000000000..e5a88d6c8c467
--- /dev/null
+++ b/solution/0000-0099/0005.Longest Palindromic Substring/Solution.c	
@@ -0,0 +1,31 @@
+char* longestPalindrome(char* s) {
+    int n = strlen(s);
+    bool** f = (bool**) malloc(n * sizeof(bool*));
+    for (int i = 0; i < n; ++i) {
+        f[i] = (bool*) malloc(n * sizeof(bool));
+        for (int j = 0; j < n; ++j) {
+            f[i][j] = true;
+        }
+    }
+    int k = 0, mx = 1;
+    for (int i = n - 2; ~i; --i) {
+        for (int j = i + 1; j < n; ++j) {
+            f[i][j] = false;
+            if (s[i] == s[j]) {
+                f[i][j] = f[i + 1][j - 1];
+                if (f[i][j] && mx < j - i + 1) {
+                    mx = j - i + 1;
+                    k = i;
+                }
+            }
+        }
+    }
+    char* res = (char*) malloc((mx + 1) * sizeof(char));
+    strncpy(res, s + k, mx);
+    res[mx] = '\0';
+    for (int i = 0; i < n; ++i) {
+        free(f[i]);
+    }
+    free(f);
+    return res;
+}
diff --git a/solution/0000-0099/0006.Zigzag Conversion/README.md b/solution/0000-0099/0006.Zigzag Conversion/README.md
index c12bad03a22aa..ad923fc0971e8 100644
--- a/solution/0000-0099/0006.Zigzag Conversion/README.md	
+++ b/solution/0000-0099/0006.Zigzag Conversion/README.md	
@@ -282,6 +282,47 @@ public class Solution {
 }
 ```
 
+#### C
+
+```c
+char* convert(char* s, int numRows) {
+    if (numRows == 1) {
+        return strdup(s);
+    }
+
+    int len = strlen(s);
+    char** g = (char**) malloc(numRows * sizeof(char*));
+    int* idx = (int*) malloc(numRows * sizeof(int));
+    for (int i = 0; i < numRows; ++i) {
+        g[i] = (char*) malloc((len + 1) * sizeof(char));
+        idx[i] = 0;
+    }
+
+    int i = 0, k = -1;
+    for (int p = 0; p < len; ++p) {
+        g[i][idx[i]++] = s[p];
+        if (i == 0 || i == numRows - 1) {
+            k = -k;
+        }
+        i += k;
+    }
+
+    char* ans = (char*) malloc((len + 1) * sizeof(char));
+    int pos = 0;
+    for (int r = 0; r < numRows; ++r) {
+        for (int j = 0; j < idx[r]; ++j) {
+            ans[pos++] = g[r][j];
+        }
+        free(g[r]);
+    }
+    ans[pos] = '\0';
+
+    free(g);
+    free(idx);
+    return ans;
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->
@@ -491,7 +532,7 @@ class Solution {
         return $result;
     }
 }
-```
+``
 
 <!-- tabs:end -->
 
diff --git a/solution/0000-0099/0006.Zigzag Conversion/README_EN.md b/solution/0000-0099/0006.Zigzag Conversion/README_EN.md
index 04390da8f24e7..a29574773c096 100644
--- a/solution/0000-0099/0006.Zigzag Conversion/README_EN.md	
+++ b/solution/0000-0099/0006.Zigzag Conversion/README_EN.md	
@@ -280,6 +280,47 @@ public class Solution {
 }
 ```
 
+#### C
+
+```c
+char* convert(char* s, int numRows) {
+    if (numRows == 1) {
+        return strdup(s);
+    }
+
+    int len = strlen(s);
+    char** g = (char**) malloc(numRows * sizeof(char*));
+    int* idx = (int*) malloc(numRows * sizeof(int));
+    for (int i = 0; i < numRows; ++i) {
+        g[i] = (char*) malloc((len + 1) * sizeof(char));
+        idx[i] = 0;
+    }
+
+    int i = 0, k = -1;
+    for (int p = 0; p < len; ++p) {
+        g[i][idx[i]++] = s[p];
+        if (i == 0 || i == numRows - 1) {
+            k = -k;
+        }
+        i += k;
+    }
+
+    char* ans = (char*) malloc((len + 1) * sizeof(char));
+    int pos = 0;
+    for (int r = 0; r < numRows; ++r) {
+        for (int j = 0; j < idx[r]; ++j) {
+            ans[pos++] = g[r][j];
+        }
+        free(g[r]);
+    }
+    ans[pos] = '\0';
+
+    free(g);
+    free(idx);
+    return ans;
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->
diff --git a/solution/0000-0099/0006.Zigzag Conversion/Solution.c b/solution/0000-0099/0006.Zigzag Conversion/Solution.c
new file mode 100644
index 0000000000000..3111a73e7035c
--- /dev/null
+++ b/solution/0000-0099/0006.Zigzag Conversion/Solution.c	
@@ -0,0 +1,36 @@
+char* convert(char* s, int numRows) {
+    if (numRows == 1) {
+        return strdup(s);
+    }
+
+    int len = strlen(s);
+    char** g = (char**) malloc(numRows * sizeof(char*));
+    int* idx = (int*) malloc(numRows * sizeof(int));
+    for (int i = 0; i < numRows; ++i) {
+        g[i] = (char*) malloc((len + 1) * sizeof(char));
+        idx[i] = 0;
+    }
+
+    int i = 0, k = -1;
+    for (int p = 0; p < len; ++p) {
+        g[i][idx[i]++] = s[p];
+        if (i == 0 || i == numRows - 1) {
+            k = -k;
+        }
+        i += k;
+    }
+
+    char* ans = (char*) malloc((len + 1) * sizeof(char));
+    int pos = 0;
+    for (int r = 0; r < numRows; ++r) {
+        for (int j = 0; j < idx[r]; ++j) {
+            ans[pos++] = g[r][j];
+        }
+        free(g[r]);
+    }
+    ans[pos] = '\0';
+
+    free(g);
+    free(idx);
+    return ans;
+}